The English language has no future tense. To refer to the future, we use various strategies with verbs in present tense (some of them auxiliaries):

I will run
I will be running
I shall run
I’m going to run
I am to run next
I’m running tomorrow
I run next Friday

Because we can conceptualise the future and it plays a big role in our lives, we talk about it often. Naturally, then, the ways we talk about it are subject to pressures of economy, resulting in contraction, e.g.:

I will run → I’ll run
I am going to run → I’m gonna/gon’ run
I’m gonna run → I’mna run → I’ma/Imma run

I’ll is acceptable in Standard English; gonna/gon’ and I’mna/I’ma/Imma are not, though you may see them in dialogue or informal writing or use some of them yourself in everyday speech – gonna is especially widespread.

Recently I came across another form: I’m on [verb]. It seems similar to I’ma and I’m gon’, but I don’t know exactly how or when it developed. Here’s the example I saw, in Elmore Leonard’s novel Mr. Paradise:

“You know who put the stuff on you?”

“Somebody close to me, his girlfriend’s punk-ass brother. Is how it goes. But listen, I’m on tell you something, I was scared.”

“I would be too,” Delsa said.

I’m on [verb] doesn’t appear to be common, at least in written English, though Google led me to this line from Kathryn Stockett’s The Help: “Today I’m on tell you bout a man from outer space.” And in GloWbE I found: “Law have mercy. I reckon I’m on do it.” (from ‘Entrepreneurs are a first world Phenomenon’ by John Egan).

Based on the few examples I’ve seen, my guess is that I’m on [verb], like I’ma, is originally and still chiefly AAVE. But I’m open to correction, and to other thoughts you might have on it. I’m on wait and see now.

Edit:

I forgot that Mark Liberman looked at this on Language Log a couple of years ago: ‘Gonna, gone, onna, a — on?‘. He begins with a different example from Elmore Leonard (“I’m on get you to the hospital”, from Raylan), and links to an older post, ‘”on” time’, that deals with the same passage I quote above.

Both posts offer helpful analysis of the construction and its various pronunciations and spellings. Thanks to @f_moncomble for the reminder.

Update:

Elmore Leonard’s book Stick (1983) has another spelling:

Barry said, somewhat louder, “Well, Cece, it’s up to you. I’m going to ask you once more to leave quietly.”

African American Vernacular English (AAVE) – without getting into its terminological complications – has a versatile and distinctive grammar for conveying aspect.* For one thing, it can omit the copulabe in some situations: She is working today → She working today.

This is known as copula deletion, zero copula, or zero auxiliary. The American Heritage Dictionarysays it’s “even more characteristic of AAVE than is invariant habitual be”. The latter, as in She be working, differs from zero copula in that it refers mainly to habitual or prolonged action.

The two constructions – zero copula and habitual/invariant be – are sometimes confused by people unfamiliar with AAVE’s syntactic subtleties, as the dictionary’s fifth edition reports:

In place of the inflected forms of be, such as is and are, used in Standard English, [AAVE] and some varieties of Southern American English may use zero copula, as in He working, or an invariant be, as in He be working, instead of the Standard English He is working. As an identifying feature of the vernacular of many African Americans, invariant be has been frequently seized on by writers and commentators trying to imitate or parody black speech. However, most imitators use it simply as a substitute for is, as in John be sitting in that chair now, without realizing that within AAVE, invariant be is used primarily for habitual or extended actions set in the present.

You can read more about the usages here, and via the previous link, both of which point to an earlier edition of the AHD.

The distinction gets a nice mention in George Pelecanos’s crime novel King Suckerman. Two characters, Rasheed and Cheek, are talking about the eponymous (fictional) blaxploitation film showing in their city:

“What new one?” said Rasheed.

“King Suckerman,” said Cheek.

Rasheed looked up. “That the one about the pimp?”

“Not any old pimp. The baddest player ever was. ‘The Man with the Master Plan Who Be Takin’ It to the Man.’”

“Who be. That’s what the ad says, huh? I bet some white man wrote that movie; produced it, too. Even wrote that line about ‘the Man’ that’s gonna get you in the theatre.”

King Suckerman hasn’t always been “takin’ it to the man” – at least not in a way worth making a film about – but he is doing so now. Who be takin’ it to the man indicates ongoing rebellion; who takin’ it to the man would imply more immediate (and hence cinematic) events. So we infer that whoever was responsible for the tagline is not a native AAVE speaker.

John Rickford says the invariant habitual be construction “has clear parallels with and possible derivations from creole ‘does be’”. Does be is a feature of Hiberno-English too, but I’ll leave that discussion for another time. Merriam-Webster’s Concise Dictionary of English Usage summarises:

The ability of a verb form or auxiliary to indicate continuation or duration of an action is called by grammarians and linguists aspect. Since English is somewhat deficient in aspect, compared to some other languages, these dialectal forms [Black English and Hiberno-English] do constitute an enrichment of the language. But they are not yet available to the writer of ordinary standard English, and no one knows if they ever will be.

*

* Grammatical aspect is defined by Huddleston and Pullum as “a verbal category mainly indicating the speaker’s view of the temporal structure of the situation the clause describes, such as whether it is habitual or complete”. For more, see SIL and Glottopedia.

The contraction I’ma (also Imma, etc., = I’m gonna) hit the spotlight in 2009 when Kanye West used it while interrupting Taylor Swift at the MTV Video Music Awards (“I’ma let you finish, but Beyoncé had one of the best videos of all time”). Parodies spread and a meme went viral.

But the phrase has been around for decades. Neal Whitman has written helpfully about its development and usage at Literal-Minded (twice) and the Visual Thesaurus; all three posts are worth reading, and there’s more at Language Log if you’re interested.

I’ma in print lags behind its occurrence in speech, but I came across it recently in Walter Mosley’s novel White Butterfly (1992). The third outing of reluctant detective Easy Rawlins, White Butterfly includes several instances of I’ma used in AAVE speech. A few examples: